Poor adherence to antiretroviral medications is responsible for 80% of the clinical failures in HIV+ individuals, and alcohol consumption is the single most commonly identified behavioral risk factor for poor adherence. For this-reason, nonadherence to antriretroviral drugs is a harmful and highly prevalent consequence of alcohol consumption. Because HIV+ individuals experience this harmful consequence at daily alcohol consumption levels that are below comparable levels for HIV- individuals and are also below standard criteria for at-risk drinking, screening criteria may need to be adapted for HIV+ individuals. However, in order for alternative criteria to be evaluated, the threshold at which alcohol consumption impacts adherence in HIV+ individuals must be characterized in more detail. The specific aims of this proposal are to quantify the shift in the alcohol consumption threshold at which alcohol impairs the adherence of HIV+ individuals compared to HIV- individuals, and to determine if subgroups of HIV+ individuals with hepatotoxicity or frailty disproportionately contribute to this threshold shift. The broad objectives of this proposal have direct relevance to the mission of NIAAA, in particular to reduce the morbidity and mortality from alcohol consumption in a population that is very susceptible to its harms (individuals with HIV). LAY LANGUAGE: Antiretroviral therapies have saved the lives of millions of individuals with HIV, but they do not work for individuals who do not take them as directed. We know from previous research that alcohol consumption can lead to poor adherence with these medications, but we do not know how much alcohol is required for this to happen. We do know that less alcohol seems to be required for HIV+ individuals than HIV- individuals. This research will enable us to determine how much alcohol is required to reduce medication adherence among HIV+ individuals, so alcohol use guidelines can be tailored appropriately, and more lives may be saved.